A paint which contains metallic pigment, such as powdered or flaked aluminum, provides the surface with a metallic luster. Most of the metallic paints are organic solvent based, but have problems in environmental pollution, working conditions and the like. Accordingly, it has been proposed and studies made to substitute water for the organic solvent.
Water, however, creates different problems. Thus, the metallic pigment is vigorously reacted with water to produce hydrogen gas which is dangerous and may cause an explosion. The problems are more serious in the automotive industries, because paint is generally stored in a closed container for a long period of time before using it.
In order to obviate the above problems, it has been proposed in Japanese Kokai Publication (unexamined) 168663/1983 to surface treat a metallic pigment with a certain organic phosphate to render its surface hydrophobic. The proposed method, however, often gives rise the agglomeration of the metallic pigment, which adversely affects the surface smoothness of the coated surface and deteriorates the adhesive properties. A large amount of a surfactant is added to the proposed coating composition to improve the above problems, but the surfactant decreases the water resistance of the coatings.